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3.Innodb体系架构之后台进程

作者:互联网

1.前言

innodb存储引擎有多个内存块,可以认为这些内存块组成了一个大的内存池,负责如下工作:

2.结构图

    

如上两幅图,第一个是官方给的整体架构图,第二幅图是工作流程图,这里重点会说一下后台进程

3.后台线程

  innodb存储引擎是多线程的模型,因此其在后台有多个不同的后台线程,负责处理不同工作任务

3.1 master thread

  master thread是一个非常核心的后台线程,主要负责将缓冲池中的数据异步刷到磁盘,保障数据的一致性,其中包括脏页的刷新、合并插入缓冲(insert buffer) undo页的回收

3.2 IO thread 

  在Innodb存储引擎中大量使用了AIO(Async IO)来处理写IO请求,这样可以极大提高了数据库的性能。而IO thread 的工作主要负责这些IO请求的回调(call back)处理,innodb 1.0版本之前共有4个IO thread ,分别是write 、read 、insert buffer和log io thread。在linux平台下,iO thread 的数量不能进行调整,但是在window平台上可以通过参数innodb_file_io_thread来增大IO thread来增大IO thread ,从innodb 1.0.x版本开始,read thread 和write thread分别增大到了4个,并且不再使用innodb_file_io_threads参数,而是分别使用innodb_read_io_thread和innodb_write_io_threads参数进行设置,

root@localhost 16:08:  [liulin]> show variables like '%io_thread%';
+-------------------------+-------+
| Variable_name           | Value |
+-------------------------+-------+
| innodb_read_io_threads  | 4     |
| innodb_write_io_threads | 4     |
+-------------------------+-------+

 这里也可以通过show engine innodb status来观察io thread

FILE I/O
--------
I/O thread 0 state: waiting for completed aio requests (insert buffer thread)
I/O thread 1 state: waiting for completed aio requests (log thread)
I/O thread 2 state: waiting for completed aio requests (read thread)
I/O thread 3 state: waiting for completed aio requests (read thread)
I/O thread 4 state: waiting for completed aio requests (read thread)
I/O thread 5 state: waiting for completed aio requests (read thread)
I/O thread 6 state: waiting for completed aio requests (write thread)
I/O thread 7 state: waiting for completed aio requests (write thread)
I/O thread 8 state: waiting for completed aio requests (write thread)
I/O thread 9 state: waiting for completed aio requests (write thread)

  可以看到IO thread 0为insert buffer thread。io thread 1为log thread.之后就是根据参数innodb_read_io_thread及innodb_write_io_threads来设置的读写线程,并且读线程iD总是小于写线程。

3.3 Purge Thread

  事务被提交后,其所使用的undolog可能不再需要,因为需要purge thread来回收已经使用并分配的undo页。在innodb1.1版本之前,purge操作仅在innodb存储引擎的master thread中完成,而从innodb1.1版本开始,purge操作可以独立到单独的线程中进行,以此来减轻master thread的工作,从而提供cpu的使用率以及提升存储引擎的性能,用户可以在配置文件中进行配置: 

root@localhost 16:15:  [liulin]> show variables like '%purge_thread%';
+----------------------+-------+
| Variable_name        | Value |
+----------------------+-------+
| innodb_purge_threads | 4     |
+----------------------+-------+
1 row in set (0.00 sec)

3.4 Page cleaner thread

  Page cleaner thread作用是将之前版本中的脏页的刷新操作都放入到单独的线程中来完成,而其目的是为了减轻master thread 的工作及对于用户查询线程的阻塞,进一步提高innodb存储引擎的性能

  

 

 

标签:架构,thread,state,aio,waiting,innodb,io,进程,Innodb
来源: https://www.cnblogs.com/zmc60/p/15223634.html